The present invention relates to a zoom camera in which the image magnification is variable in accordance with the object distance.
Cameras having a zoom lens system capable of photographing with constant image magnification are conventionally known.
For example, in an apparatus shown in Japanese Laid-Open Patent Publication (Tokkaisho) No. 53-113527, a position of a variator lens group with which images of a constant image magnification can be obtained even if the object distance changes is computed and set based on the object distance and the image magnification.
Further, in an art shown in Japanese laid-Open Patent Publication No. 55-64204, the rotation angles and the divisions of scales of a focus ring and a zoom ring respectively are so designed that the two rings can integratedly rotate so as to obtain a constant image magnification. In this prior art publication, it is described that if slightly different image magnifications, not an absolutely fixed one, are preferred, other designs can be made in order to obtain such image magnifications. However, such designs have not been disclosed concretely there.
Further, in the abovementioned two prior arts, no range of the object distance wherein constant image magnification can be obtained has been disclosed.
Further, in an art shown in Japanese Laid-Open Patent Publication No. 54-39144, a compensator lens group can make a predetermined movement different from the movement of a variator lens group so that photographing with constant image magnification can be achieved only by the zooming operation. In this prior art publication, it is described that a constant image magnification is obtained in the range of the photgraphing distance D from 1.5 m to 8.8 m. However, how to treat the image magnification at the photographing distance D below and above this range has not been disclosed.
Further, in an art shown in Japanese Patent Publication (Tokkosho) No. 51-27577, a focus ring and a zoom ring are interlocked with each other by providing a zoom cam between the two rings which meets the relation represented by a formula M=f/x (M=image magnification, x=photographing distance; f=focal length of zoom lens) so that photographing with constant image magnification can be achieved only by the focusing operation. In this prior art published, it is described that a constant image magnification is obtained in the range of the photographing distance D from 2 m to 10 m. However, how to treat the image magnification at the photographing distance D below and above this range has not been disclosed.
Further, in an art shown in Japanese Laid-Open Patent Publication No. 61-38917, the focal length f of a zoom lens is automatically controlled so as to make the value f/D to be constant. And if the photographing distance D is above a range in which zooming is executed interlockedly with auto-focusing, the focal length is controlled to be at the closest zoom position and an indication OUT OF RANGE is displayed.
Further, in an art shown in Japanese Laid-Open Utility Model Publication No. 62-69224, when the photographing distance detected based on a distance measuring signal becomes large, zooming up (closeup) is executed, and when the photographing distance becomes small, zooming has no relation with the photographing distance.
Further, in an art shown in Japanese Laid-Open Patent Publication No. 60-4911, a focusing mechanism and an image magnification changing mechanism are mechanically interlocked, so that the image magnification is set to be high on the longest focal length condition and low on the shortest focal length condition. And an embodiment is described in which a zoom lens with a focal length from 80 mm to 200 mm is used and the focusing mechanism and the image magnification changing mechanism are so interlocked that when the focal length is 80 mm, an object at the object distance of 20 m is in in-focus and when the focal length is 200 mm, an object at the object distance of 40 m is in in-focus.
Further, in an art shown in Japanese Laid-Open Patent Publication No. 62-118328, pictures having a suitable size of object image are obtained based on distance data. And an example is shown in which when an object to be photographed is at a far distance or at a middle distance, a focal length setting switch is turned to a longer focal length, and when an object is at a close distance, it is turned to a shorter focal length.
Futhermore, in an art shown in Japanese Patent Publication No. 60-1602, the focal length is controlled in a feed-back manner by treating logarithms of the constant image magnification, the photographing distance and the focal length.
In this connection, zooming has a relation to the framing of images to be photographed, and it is judged by a print or a negative film whether a zooming is good or bad. However, generally it is very difficult for a user to judge at what focal length position to stop zooming operation. Accordingly, if basic image magnification is proposed to users by setting focal lengths variable according to predetermined program relating to a photographing distance, a more desirable picture can be taken by an easy operation in auto-zooming. And as a result, zooming becomes truly easy to use.